Tuesday, June 28, 2011

Latest Research on the History of Antarctica

Researchers ascertained the exact species of plants that existed on the Antarctic Peninsula over the past 36 million years during a three-year examination of thousands of grains of fossilized pollen, including this grain from the tree Nothofagus fusca. (Credit: S. Warny/LSU)

Fossilized Pollen Reveals Climate History of Northern Antarctica: Tundra Persisted Until 12 Million Years Ago

ScienceDaily (June 27, 2011) — A painstaking examination of the first direct and detailed climate record from the continental shelves surrounding Antarctica reveals that the last remnant of Antarctic vegetation existed in a tundra landscape on the continent's northern peninsula about 12 million years ago.

The research, which was led by researchers at Rice University and Louisiana State University, appears online this week and will be featured on the cover of the July 12 issue of the Proceedings of the National Academy of Sciences.

The new study contains the most detailed reconstruction to date of the climatic history of the Antarctic Peninsula, which has warmed significantly in recent decades. The rapid decline of glaciers along the peninsula has led to widespread speculation about how the rest of the continent's ice sheets will react to rising global temperatures.

"The best way to predict future changes in the behavior of Antarctic ice sheets and their influence on climate is to understand their past," said Rice University marine geologist John Anderson, the study's lead author. The study paints the most detailed picture to date of how the Antarctic Peninsula first succumbed to ice during a prolonged period of global cooling.

In the warmest period in Earth's past 55 million years, Antarctica was ice-free and forested. The continent's vast ice sheets, which today contain more than two-thirds of Earth's freshwater, began forming about 38 million years ago. The Antarctic Peninsula, which juts farther north than the rest of the continent, was the last part of Antarctica to succumb to ice. It's also the part that has experienced the most dramatic warming in recent decades; its mean annual temperatures rose as much as six times faster than mean annual temperatures worldwide.

"There's a longstanding debate about how rapidly glaciation progressed in Antarctica," said Sophie Warny, a Louisiana State University geologist who specializes in palynology (the study of fossilized pollen and spores) and led the palynological reconstruction. "We found that the fossil record was unambiguous; glacial expansion in the Antarctic Peninsula was a long, gradual process that was influenced by atmospheric, tectonic and oceanographic changes."

Warny, her students and colleague Rosemary Askin were able to ascertain the exact species of plants that existed on the peninsula over the past 36 million years after a painstaking, three-year examination of thousands of individual grains of pollen that were preserved in muddy sediments beneath the sea floor just off the coast.
"The pollen record in the sedimentary layers was beautiful, both in its richness and depth," Warny said. "It allowed us to construct a detailed picture of the rapid decline of the forests during the late Eocene -- about 35 million years ago -- and the widespread glaciation that took place in the middle Miocene -- about 13 million years ago."

Obtaining the sedimentary samples wasn't easy. The muddy treasure trove was locked away beneath almost 100 feet of dense sedimentary rock. It was also off the coast of the peninsula in shallow waters that are covered by ice most of the year and beset by icebergs the rest. Anderson, a veteran of more than 25 research expeditions to Antarctica, and colleagues spent more than a decade building a case for the funding to outfit an icebreaker with the right kind of drilling equipment to bore through the rock.

In 2002, the National Science Foundation (NSF) funded the project, which was dubbed SHALDRIL. Three years later, the NSF research vessel Nathaniel B. Palmer left on the first of two drilling cruises.

"It was the worst ice year that any of us could remember," Anderson said. "We'd spend most of a day lowering drill string to the ocean floor only to pull it back up to get out of the way of approaching icebergs."
The next year was little better, but the SHALDRIL team managed to obtain enough core samples to cover the past 36 million years, thanks to the logistical planning of marine geologist Julia Wellner and to the skill of the drilling crew. By end of the second season, Anderson said, the crew could drill as much as a meter every five minutes.

Reconstructing a detailed climate record from the sample was another Herculean task. In addition to the three-year palynological analysis at LSU, University of Southampton palaeoceanographer Steven Bohaty led an effort to nail down the precise age of the various sediments in each core sample. Wellner, now at the University of Houston, examined the characteristics of the sediments to determine whether they formed below an ice sheet, in open marine conditions or in a combined glacial-marine setting. Other members of the team had to count, categorize and even examine the surface texture of thousands of sand grains that were preserved in the sediments. Gradually, the team was able to piece together a history of how much of the peninsula was covered by glaciers throughout the past 36 million years.

"SHALDRIL gave us the first reliable age constraints on the timing of ice sheet advance across the northern peninsula," Anderson said. "The rich mosaic of organic and geologic material that we found in the sedimentary record has given us a much clearer picture of the climatic history of the Antarctic Peninsula. This type of record is invaluable as we struggle to place in context the rapid changes that we see taking place in the peninsula today."

The study was funded by grants from the NSF's Office of Polar Programs to Anderson and Warny. Study co-authors include Wellner; Askin; Bohaty; Alexandra Kirshner, Tyler Smith and Fred Weaver, all of Rice; Alexander Simms and Daniel Livsey, both of the University of California, Santa Barbara; Werner Ehrmann of the University of Leipzig; Lawrence Lawver of the University of Texas at Austin; David Barbeau of the University of South Carolina; Sherwood Wise and Denise Kulhenek, both of Florida State University; and Wojciech Majewski of the Polish Academy of Sciences.
Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Rice University.

Journal Reference:
  1. John B. Anderson, Sophie Warny, Rosemary A. Askin, Julia S. Wellner, Steven M. Bohaty, Alexandra E. Kirshner, Daniel N. Livsey, Alexander R. Simms, Tyler R. Smith, Werner Ehrmann, Lawrence A. Lawver, David Barbeau, Sherwood W. Wise, Denise K. Kulhenek, Fred M. Weaver, Wojciech Majewski. Progressive Cenozoic cooling and the demise of Antarctica’s last refugium. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1014885108

Rice University (2011, June 27). Fossilized pollen reveals climate history of northern Antarctica: Tundra persisted until 12 million years ago. ScienceDaily. Retrieved June 28, 2011, from http://www.sciencedaily.com­ /releases/2011/06/110627163508.htm

Monday, June 27, 2011

Body Temperatures of Dinosaurs Measured for First Time: Some Dinosaurs Were as Warm as Most Modern Mammals

Caltech geochemists Rob Eagle (left) and John Eiler adjust equipment used to analyze the isotopic concentrations in dinosaur teeth and reveal the body temperature of the extinct creatures. (Credit: Caltech / Lance Hayashida)

ScienceDaily (June 23, 2011) — Were dinosaurs slow and lumbering, or quick and agile? It depends largely on whether they were cold or warm blooded. When dinosaurs were first discovered in the mid-19th century, paleontologists thought they were plodding beasts that had to rely on their environments to keep warm, like modern-day reptiles. But research during the last few decades suggests that they were faster creatures, nimble like the velociraptors or T. rex depicted in the movie Jurassic Park, requiring warmer, regulated body temperatures like in mammals.

Now, a team of researchers led by the California Institute of Technology (Caltech) has developed a new approach to take body temperatures of dinosaurs for the first time, providing new insights into whether dinosaurs were cold or warm blooded. By analyzing isotopic concentrations in teeth of sauropods, the long-tailed, long-necked dinosaurs that were the biggest land animals to have ever lived -- think Apatosaurus (also known as Brontosaurus) -- the team found that the dinosaurs were about as warm as most modern mammals.

"This is like being able to stick a thermometer in an animal that has been extinct for 150 million years," says Robert Eagle, a postdoctoral scholar at Caltech and lead author on the paper to be published online in the June 23 issue of Science Express.

"The consensus was that no one would ever measure dinosaur body temperatures, that it's impossible to do," says John Eiler, a coauthor and the Robert P. Sharp Professor of Geology and professor of geochemistry. And yet, using a technique pioneered in Eiler's lab, the team did just that.

The researchers analyzed 11 teeth, dug up in Tanzania, Wyoming, and Oklahoma, that belonged to Brachiosaurus brancai and Camarasaurus. They found that the Brachiosaurus had a temperature of about 38.2 degrees Celsius (100.8 degrees Fahrenheit) and the Camarasaurus had one of about 35.7 degrees Celsius (96.3 degrees Fahrenheit), warmer than modern and extinct crocodiles and alligators but cooler than birds. The measurements are accurate to within one or two degrees, Celsius.

"Nobody has used this approach to look at dinosaur body temperatures before, so our study provides a completely different angle on the longstanding debate about dinosaur physiology," Eagle says.

The fact that the temperatures were similar to those of most modern mammals might seem to imply that dinosaurs had a warm-blooded metabolism. But, the researchers say, the issue is more complex. Because large sauropod dinosaurs were so huge, they could retain their body heat much more efficiently than smaller mammals like humans. "If you're an animal that you can approximate as a sphere of meat the size of a room, you can't be cold unless you're dead," Eiler explains. So even if dinosaurs were "cold blooded" in the sense that they depended on their environments for heat, they would still have warm body temperatures.

"The body temperatures we've estimated now provide a key piece of data that any model of dinosaur physiology has to be able to explain," says Aradhna Tripati, a coauthor who's an assistant professor at UCLA and visiting researcher in geochemistry at Caltech. "As a result, the data can help scientists test physiological models to explain how these organisms lived."

The measured temperatures are lower than what's predicted by some models of body temperatures, suggesting there is something missing in scientists' understanding of dinosaur physiology. These models imply dinosaurs were so-called gigantotherms, that they maintained warm temperatures by their sheer size. To explain the lower temperatures, the researchers suggest that the dinosaurs could have had some physiological or behavioral adaptations that allowed them to avoid getting too hot. The dinosaurs could have had lower metabolic rates to reduce the amount of internal heat, particularly as large adults. They could also have had something like an air-sac system to dissipate heat. Alternatively, they could have dispelled heat through their long necks and tails.
Previously, researchers have only been able to use indirect ways to gauge dinosaur metabolism or body temperatures. For example, they infer dinosaur behavior and physiology by figuring out how fast they ran based on the spacing of dinosaur tracks, studying the ratio of predators to prey in the fossil record, or measuring the growth rates of bone. But these various lines of evidence were often in conflict. "For any position you take, you can easily find counterexamples," Eiler says. "How an organism budgets the energy supply that it gets from food and creates and stores the energy in its muscles -- there are no fossil remains for that," he says. "So you just sort of have to make your best guess based on indirect arguments."

But Eagle, Eiler, and their colleagues have developed a so-called clumped-isotope technique that shows that it is possible to take body temperatures of dinosaurs -- and there's no guessing involved. "We're getting at body temperature through a line of reasoning that I think is relatively bullet proof, provided you can find well-preserved samples," Eiler says. In this method, the researchers measure the concentrations of the rare isotopes carbon-13 and oxygen-18 in bioapatite, a mineral found in teeth and bone. How often these isotopes bond with each other -- or "clump" -- depends on temperature. The lower the temperature, the more carbon-13 and oxygen-18 tend to bond in bioapatite. So measuring the clumping of these isotopes is a direct way to determine the temperature of the environment in which the mineral formed -- in this case, inside the dinosaur.

"What we're doing is special in that it's thermodynamically based," Eiler explains. "Thermodynamics, like the laws of gravity, is independent of setting, time, and context." Because thermodynamics worked the same way 150 million years ago as it does today, measuring isotope clumping is a robust technique.

Identifying the most well-preserved samples of dinosaur teeth was one of the major challenges of the analysis, the researchers say, and they used several ways to find the best samples. For example, they compared the isotopic compositions of resistant parts of teeth -- the enamel -- with easily altered materials -- dentin and fossil bones of related animals. Well-preserved enamel would preserve both physiologically possible temperatures and be isotopically distinct from dentin and bone.

The next step is to take temperatures of more dinosaur samples and extend the study to other species of extinct vertebrates, the researchers say. In particular, taking the temperature of unusually small and young dinosaurs would help test whether dinosaurs were indeed gigantotherms. Knowing the body temperatures of more dinosaurs and other extinct animals would also allow scientists to learn more about how the physiology of modern mammals and birds evolved.

In addition to Eagle, Eiler, and Tripati, the other authors are Thomas Tütken from the University of Bonn, Germany; Caltech undergraduate Taylor Martin; Henry Fricke from Colorado College; Melissa Connely from the Tate Geological Museum in Casper, Wyoming; and Richard Cifelli from the University of Oklahoma. Eagle also has a research affiliation with UCLA.

This research was supported by the National Science Foundation and the German Research Foundation.
Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by California Institute of Technology. The original article was written by Marcus Woo.

Journal Reference:
  1. Robert A. Eagle, Thomas Tütken, Taylor S. Martin, Aradhna K. Tripati, Henry C. Fricke, Melissa Connely, Richard L. Cifelli, John M. Eiler. Dinosaur Body Temperatures Determined from Isotopic (13C-18O) Ordering in Fossil Biominerals. Science, 2011; DOI: 10.1126/science.1206196

California Institute of Technology (2011, June 23). Body temperatures of dinosaurs measured for first time: Some dinosaurs were as warm as most modern mammals. ScienceDaily. Retrieved June 27, 2011, from http://www.sciencedaily.com­ /releases/2011/06/110623141312.htm

Friday, June 24, 2011

Why Penguins Are Afraid of the Dark

Enlarge Image

on 23 June 2011

Like daily commuters, Adélie and emperor penguins are up at dawn, catching krill and fish in Antarctic waters, and back home to shore at dusk. Yet the food they prefer to dine on is easiest to catch after dark. Most researchers assumed that penguins had poor nighttime vision, which was why they stayed out of the water after dusk.

But in a new study, two marine ecologists argue that the penguins actually have no trouble seeing in the dark. Instead, they say, penguins head for shore at night because they cannot gauge the risk of being eaten by leopard seals or killer whales. Even their migration patterns, when they move from some of the Southern Ocean's most productive waters into those that are marginal, are likely shaped by the fear of predators. "They would rather be hungry" than dead, says the study's lead author, David Ainley, a marine ecologist at H. T. Harvey and Associates, an ecological consulting firm in Los Gatos, California.

To show that the penguins can see in the dark, Ainley and his colleague, Grant Ballard, a marine ecologist at PRBO Conservation Science, a conservation organization in Petaluma, California, outfitted 65 adult Adélie penguins with time-depth recorders. The devices, which register depth and light every second, were taped to the lower back, so that they caused the least amount of drag. Data collected on nearly 22,000 of the birds' foraging dives showed that most were hunting prey at 50 to 100 meters below the surface, where the water is quite dark—akin to early night. The birds also made a significant number of dives into deeper, darker waters, where they can forage successfully.

Although the two researchers did not collect similar data on emperor penguins, other scientists have shown that these birds dive even deeper, into waters more than 500 meters below the surface. "At that depth, it's absolutely black," Ainley says.

So why won't the penguins hunt at night? Ainley and Ballard note that leopard seals, which regularly kill both species of penguins, rest at midday, making it safer for penguins to hunt during this time. Even then, the penguins are cautious; they stay in the water only long enough to feed, and they're adept at remaining motionless when they're on thin ice and spot a leopard seal. At the Ross Island colony in Antarctica, Adélies that land at the far end of the island will even walk the 5 kilometers to reach their home rather than enter the water again and swim, which would get them back faster.

Killer whales may also be a problem. Although they have not been actually observed taking either Adélie or emperor penguins, cetacean researchers suspect that they do, because orcas have been seen killing and eating other penguin species in Antarctic and subantarctic waters. What's more, certain types of killer whales are prey specialists, feeding only on marine mammals and seabirds, and in the Antarctic these orcas are known to visit areas near emperor penguin colonies.

Fear of predators doesn't just affect the penguins' daily activities, however. It also influences the birds' migration patterns, Ainley and Ballard report this week in Polar Biology. Emperor penguin adults and chicks leave their colonies in the late Antarctic summer. But instead of heading to the closest and richest waters, they swim north to far less productive waters. During that journey, other researchers have noted, some 20% to 30% of juvenile emperors are killed.

"We don't have the evidence, but it is very likely killer whales are taking them," Ainley says. Similarly, the Adélie penguins migrate to northern areas in the Antarctic winter, presumably because they do not want to live in total darkness in the south. It's more difficult to spot predators during this period, Ainley says.
"They've provided a convincing argument for what look like very strange behaviors" on the part of the penguins, says Aaron Wirsing, a behavioral ecologist at the University of Washington, Seattle. "It's another good example of how widespread the ecology of fear is in nature," adds William Ripple, an ecologist at Oregon State University in Corvallis, who has studied the effects of fear on the elk population in Yellowstone National Park following the reintroduction of gray wolves. "Predators, and the fear they instill, are major shapers of ecosystems," he says.


Saturday, June 4, 2011

A Message from Dr. Dee Boersma


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Friday, June 3, 2011

Coordinated Movements in a Penguin Huddle

Coordinated movements in an emperor penguin huddle: (A) Observed field of view of the emperor penguin colony. The image shows several huddles and individual penguins. The density of penguins in huddles is approximately 21 animals per square meter. (B) The penguins' yellow and white face patch was used to track individual animals. (C) Typical trajectory of a penguin during huddle movements. Motionless periods are interrupted by intermittent small steps that lead over time to a reorganization of the entire huddle. (D) Positions of penguins tracked over 4 hours show a collective huddle movement as indicated by red arrows (movies available online). (E) Trajectories from neighboring penguins with similar vertical (y) positions show correlated steps in the horizontal (x) direction. The speed of the propagating wave is indicated by the slope of the red line. (Credit: Daniel P. Zitterbart, Barbara Wienecke, James P. Butler, Ben Fabry. Coordinated Movements Prevent Jamming in an Emperor Penguin Huddle. PLoS ONE, 2011; 6 (6): e20260 DOI: 10.1371/journal.pone.0020260)

Keeping Warm: Coordinated Movements in a Penguin Huddle

ScienceDaily (June 2, 2011) — To survive temperatures below -50 ° C and gale-force winds above 180 km/h during the Antarctic winter, Emperor penguins form tightly packed huddles and, as has recently been discovered -- the penguins actually coordinate their movements to give all members of the huddle a chance to warm up.

Physicist Daniel P. Zitterbart from the University of Erlangen-Nuremberg, Germany, recently spent a winter at Dronning Maud Land in the Antarctic, making high-resolution video recordings of an Emperor penguin colony. Together with biophysicist Ben Fabry from Erlangen University, physiologist James P. Butler from Harvard University, and marine biologist Barbara Wienecke from the Australian Antarctic Division, they found that penguins in a huddle move in periodic waves to continuously change the huddle structure. This movement allows animals from the outside to enter the tightly packed huddle and to warm up.
The results have now been published in the journal PLoS ONE.
The survival techniques of Emperor penguins have long intrigued scientists. One unresolved question was how penguins move to the inside of a huddle when the animals stand packed so tightly that no movement seems possible. Daniel P. Zitterbart and his team discovered that penguins solve this problem by moving together in coordinated periodic waves. This was observed by tracking the positions of hundreds of penguins in a colony for several hours. The periodic waves are invisible to the naked eye as they occur only every 30-60 seconds and travel with a speed of 12 cm/s through the huddle. Although small, over time they lead to large movements that are reminiscent of dough during kneading. The authors compare the formation of a huddle to "colloidal jamming" and the periodic waves to a "temporary fluidization." "Our data show that the dynamics of penguin huddling is governed by intermittency and approach to kinetic arrest in striking analogy with inert non-equilibrium systems, including soft glasses and colloids."
Daniel P. Zitterbart is currently developing a remote-controlled observatory to study penguins all year round. He hopes to witness the reversal of the dramatic decline in penguin colony sizes that is occurring in all areas of the Antarctic.

Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Public Library of Science, via EurekAlert!, a service of AAAS.

Journal Reference:
  1. Daniel P. Zitterbart, Barbara Wienecke, James P. Butler, Ben Fabry. Coordinated Movements Prevent Jamming in an Emperor Penguin Huddle. PLoS ONE, 2011; 6 (6): e20260 DOI: 10.1371/journal.pone.0020260

Public Library of Science (2011, June 2). Keeping warm: Coordinated movements in a penguin huddle. ScienceDaily. Retrieved June 3, 2011, from http://www.sciencedaily.com­ /releases/2011/06/110601171614.htm